Guard Independence and Constraint-Preserving Snapshot Isolation

Abstract. A method for detecting potential violations of integrity constraints of concurrent transactions running under snapshot isolation (SI) is presented. In contrast to methods for ensuring full serializability under snapshot isolation, violations of integrity constraints may be detected by examining certain read-write interaction of only two transactions at a time. The method, called constraint-preserving snapshot isolation (CPSI), thus provides greater isolation than ordinary SI in that results do not violate any integrity constraints, while requiring substantially less overhead, and involving fewer false positives, than typical for enhancements to SI which guarantee full serializable isolation.